Internal combustion engine

Abstract

A two-stroke internal combustion engine is disclosed having opposed cylinders, each cylinder having a pair of opposed pistons, with all the pistons connected to a common central crankshaft. The inboard pistons of each cylinder are connected to the crankshaft with pushrods and the outboard pistons are connected to the crankshaft with pullrods. Each opposed cylinder further comprises an integrated scavenge pump for providing positive intake pressure. This configuration results in a compact engine with a very low profile, in which the free mass forces can be substantially balanced. The engine configuration also allows for asymmetrical timing of the intake and exhaust ports through angular positioning of the journals on the crankshaft.

Description

RELATED APPLICATION [0001] This application claims priority from U.S. Provisional Application Ser. No. 60 / 482,772, filed Jun. 25, 2003, and the contents of which are hereby incorporated by reference as if recited in full herein for all purposes.FIELD OF THE INVENTION [0002] The present invention relates generally to two-stroke internal combustion engines, and more specifically to a two-stroke internal combustion engine having a pair of opposed cylinders, each cylinder having a pair of opposed pistons. BACKGROUND OF THE INVENTION [0003] The design and production of internal combustion engines for the automotive and light aircraft industries are well-developed fields of technology. To be commercially viable, any new engine configuration must, without sacrificing performance, provide significant improvements in the areas of energy and raw material conservation (especially the improvement of fuel consumption), environmental protection and pollution control, passenger safety and comfort,...

AI Technical Summary

Benefits of technology

[0015] Embodiments of the present invention provide a two cylinder two-stroke internal combustion engine having improved efficiency, a reduced height profile and lower weight for improved installation suitability, substantially total dynamic balance, and mechanical simplicity for reduced production costs.

[0019] In accordance with embodiments of the invention, each inner piston on its end remote from the combustion chamber has a smooth end face that is convexly curved in a plane perpendicular to the longitudinal axis of the crankshaft. An associated pushrod has a concavely shaped outer end surface that slidingly engages the curved end face of the inner piston. This pushrod configuration serves to effectively lengthen the pushrods; thereby reducing friction losses and improving dynamic balance.

Problems solved by technology

An improvement in one of these areas at the expense of any other is commercially unacceptable.

Despite the promise of external continuous combustion technologies such as Stirling engines or fuel cells with electric motors to eventually provide low-emission high-efficiency engines for automobiles and light aircraft, these technologies will not be viable alternatives to internal combustion engines in the foreseeable future due to their inherent disadvantages in weight, space, drivability, energy density and cost.

The need for at least four cylinders to achieve a suitable rate of power stroke production dictates the size and shape of this engine, and therefore also greatly limits the designers' options on how the engine is placed within the vehicle.

The small cylinders of these engines are typically not optimal for efficient combustion or the reduction of raw emissions.

The four cylinder in-line configuration also has drawbacks with respect to passenger comfort, since there are significant unbalanced free-mass forces which result in high noise and vibration levels.

Two-stroke engines, however, have seen limited use because of several perceived drawbacks.

Two-stroke engines have a disadvantage in mean effective pressure (i.e., poorer volumetric efficiency) over four-stroke engines because a significant portion of each stroke must be used for the removal of the combustion products of the preceding power stroke (scavenging) and the replenishment of the combustion air, and is therefore lost from the power stroke.

Scavenging is also inherently problematic, particularly when the engine must operate over a wide range of speeds and load conditions.

Two-stroke compression-ignition (Diesel) engines are known to have other drawbacks as well, including poor starting characteristics and high particulate emissions.

The largest sources of friction loss in current production automotive engines, accounting for approximately half of all friction losses, are the result of the lateral forces produced by the rotating connecting rods acting on the pistons, pushing them against the cylinder walls.

Another significant source of friction loss in current production engines are the large forces acting on the crankshaft main bearings.

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